Banerjerk, I take it he did not have any mechanical problems at the time - right?
If it's just his stupidity of riding in the dark without lights that was an issue, then ask yourself this: "Should I stop all cars and buckle their seatbelts for them?"
Sounds like this guy chose to do a stupid and dangerous thing. If you rode along with him you might have been able to light his way – but you would not have made him more visible and could have endangered yourself by being close to him when a car “swerves to miss the black blob next to the cyclists”.
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It's better to cycle through life than to drive by it.